GCSE Biology - Food Tests Practicals
Food Tests for GCSE Biology Practical
Overview of Food Tests
- The video covers essential food tests for GCSE Biology practicals, including the Benedict's test for sugars, iodine test for starch, Biuret test for proteins, and Sudan 3 test for lipids. Additionally, it mentions the Emulsion test for lipids specific to the Edexcel course.
Preparing Food Samples
- To prepare a food sample, break up the food using a mortar and pestle. Then mix the crushed food with distilled water in a beaker and stir with a glass rod until some dissolves.
- Filter the solution through filter paper in a funnel to remove solid bits of food. The resulting solution will be used for various food tests.
Benedict's Test for Reducing Sugars
- Transfer 5 cm³ of the prepared sample into a test tube and set up a water bath at 75°C. Add about 10 drops of Benedict's solution to the sample.
- Place the test tube in the water bath for 5 minutes using a holder. If reducing sugars are present, the color changes from blue to green, yellow, or brick red based on concentration.
Iodine Test for Starch
- For starch testing, add 5 cm³ of your food sample to another test tube along with a few drops of iodine solution.
- A positive result is indicated by a color change from browny-orange to blue-black after gently shaking.
Biuret Test for Proteins
- In this protein test, use 2 cm³ of your sample and add an equal amount (2 cm³) of Biuret solution.
- A positive result shows as a color change from blue to pink or purple; Edexcel students may need potassium hydroxide followed by copper sulfate instead.
Sudan 3 Test and Emulsion Test for Lipids
- For lipids using Sudan 3: take 5 cm³ of unfiltered sample and add three drops of Sudan 3 stain; shake gently. A bright red layer indicates lipid presence.